Revision joint replacement, wear particles, and macrophage polarization
Introduction
Total joint replacement (TJR) is a successful operation for patients suffering from disabling arthritis and other degenerative conditions. However, wear of artificial joints occurs in association with the level of activity and duration of implantation. TJR failure is often associated with osteolysis and is a long-term complication that may require revision surgery [1], [2], [3], [4], [5]. Production of wear particles which are biologically active and indigestible incites an innate inflammatory reaction that may lead to periprosthetic bone loss, implant loosening and pathological fracture through osteolytic bone [4], [5], [6], [7], [8]. Particles are phagocytosed by monocyte/macrophage lineage cells, leading to their proliferation, differentiation, and activation [1], [9], [10]. These events lead to intracellular signal transduction involving activation of transcription factor NFkB and nuclear translocation, which up-regulate gene expression mechanisms for pro-inflammatory cytokines, chemokines, and other substances [5], [11], [12]. The end result is the disruption of the homeostatic balance between bone formation and resorption [5], [11], [12].
A current hypothesis suggests that macrophage activation in osteolysis may culminate in a specific phenotype, with polarization to either M1 or M2 profile, due to the undifferentiated nature of monocyte/macrophage precursors, and the microenvironment of cell activation [9], [13]. Studies also suggest that there may be epigenetic control of macrophage polarization, suggesting a possible genetic predisposition for osteolysis [14], [15], [16]. Specifically, this hypothesis suggests that wear particles initiate the migration of monocyte/macrophage precursors to the local site of particle production, and subsequent differentiation and activation to a classical M1 phenotype that initially promotes acute inflammation. This acute inflammatory state overcomes the anti-inflammatory environment supported by alternatively activated M2 macrophages that normally promotes bone healing, debris scavenging, wound healing, and angiogenesis [11], [12].
The cytokine production profiles of M1 and M2 macrophages differ significantly and can be used to identify different predominant populations in a specific clinical situation. M1 macrophages produce primarily pro-inflammatory mediators, including TNF-α, IL-1, IL-6, and type 1 interferon, as well as IL-12 and IL-23, with the expression of inducible nitric oxide synthase (iNOS) and HLA-DR [17], [18], [19]. In contrast, M2 macrophages produce low levels of IL-12 and pro-inflammatory cytokines. The M2 profile is characterized by increased IL-4, IL-10, and IL-13 production, and expression of CCL1, CCL18, FIZZ1, mammalian chitinase Ym1, Arginase 1, CD163, and chitotriosidase [11], [12], [20], [21]. This differential cytokine production and receptor expression can be used to characterize which macrophages are present in a clinical situation. Once individual populations of M1 and M2 macrophages are identified, the cytokine profiles induced by pro-inflammatory stimuli such as lipopolysaccharide (LPS) or wear particles may be used to confirm the phenotype of the macrophages [22]. Lipopolysaccharide is a particularly relevant stimulus to joint replacement, as Greenfield and colleagues have demonstrated the presence of LPS in some retrieved tissues [23], [24], [25], [26].
The overall goal of this research was to identify macrophage populations in retrieved tissues from primary total joint replacement compared to revision surgeries with wear-particle-associated inflammation. First we hypothesized that there is a higher ratio of M1/M2 macrophages in tissues harvested from patients undergoing revision joint replacement compared to synovial tissues from patients undergoing primary joint replacement. We then questioned whether it was possible to isolate and modulate macrophage populations in vitro to selectively enhance an M2 profile in response to the inflammatory stimuli LPS and polymethyl-methacrylate (PMMA) particles by adding IL-4 to differentiate uncommitted macrophages towards a M2 phenotype [11]. We tested these hypotheses using immunohistochemistry, Western blot analysis, flow cytometry, and enzyme-linked immunosorbent (ELISA) assay of culture supernatants.
Section snippets
Tissue collection
This research was approved by the Stanford University School of Medicine’s Administrative Panel on Human Subjects in Medical Research. Synovium was collected during primary TJR and periprosthetic tissues during revision joint replacement. Periprosthetic tissues were obtained from patients with radiographic evidence of osteolysis who underwent revision total hip or knee arthroplasty in the absence of infection (all tissues were aerobic and anaerobic culture negative). We collected synovium from
Clinical investigation
The results are presented in the context of two experimental research plans. The first focuses on the clinical characterization of the synovium and pseudomembrane retrieval tissues by immunohistochemistry and Western blotting. Initial studies focused on the differential expression of M1 and M2 macrophages in human synovial tissue as compared to periprosthetic tissues.
Discussion
The purpose of this study was to determine whether wear particles associated with joint replacements influenced macrophage polarization. The experimental plan used human tissue retrievals and in vitro studies with isolated murine monocyte/macrophages. Although the revision surgery cases represent a variety of implant and wear debris types, which may be seen as a weakness of the study, as all cases demonstrated the same principles of macrophage polarization in response to wear debris, this gives
Acknowledgements
This research was supported by the Ellenburg Chair in Surgery at Stanford University and the Medical Scholars Program at Stanford University School of Medicine. We would like to thank Dr Nidhi Bhutani, Matt Decker, Subbus Dhulipala, and Andrew Peterman for their contributions.
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